1. Field of the Invention
The invention relates generally to well drilling, investigation, and maintenance. More particularly, the invention relates to a clamping device and methods for adding components (e.g. drill pipe, stabilizers, other bottom hole components) to, and removing them from, a downhole well string. Still more particularly, the present invention relates to gripping and suspending well string components from above a borehole.
2. Background of the Technology
Drilling for hydrocarbons is an example of an operation involving use of a downhole well string in a borehole formed in the earth. In the case of drilling, the downhole string is referred to as a drill string. Other types of downhole strings are known in the oil and gas industry, e.g., completion string for completion jobs and production string for production jobs. Drilling involves inserting a drill string into a borehole and operating the drill string to drill the borehole. The borehole is typically drilled using a top drive or a rotary table arranged above the borehole to engage the top of the drill string and to rotate it. As the drill string is rotated, a drill bit at the bottom of the drill string cuts into the earth.
During drilling operations, it is necessary from time to time to add or remove lengths of drill pipe (“joints”) to/from the drill string. One reason for adding joints is to lengthen the drill string to enable it to drill deeper into the earth. One reason for removing joints from the drill string is to retrieve the drill string from the borehole so that the drill bit can be changed or so other changes can be made to the bottom-hole assembly that is appended to the bottom of the drill string.
Joints can be added to or removed from the drill string in the form of stands, where each stand is made up of multiple connected joints. While a joint, stand or other component is being added to or removed from the drill string, the entire weight of the drill string must be suspended from a position above the borehole. Conventionally, a suspension assembly arranged in the rotary table is used to suspend the drill string and includes components such as bushings, insert bowls, and slips. Typically, a bushing is mounted in an opening in the rotary table. The bushing has an opening which receives the drill string. Slips are inserted between the bushing and the component of the drill string that is adjacent to the bushing. Slips are wedges and may have gripping surfaces, e.g., teeth, for gripping the drill string component. The slips rest on a tapered seat provided by the bushing. In some cases, the slips will not completely bridge the gap between the bushing and the drill string, and so an insert bowl is inserted between the bushing and the drill string to enable the slips to engage the drill string component. Due to their wedged shape, the slips exert a radial clamping force on the suspended string. The clamping force is dependent on the weight of the suspended string, such that as more joints are added to the string, the weight and the clamping force increase. This effect can result in excessive clamping force and can limit the length of string that can be suspended without crushing the component that is directly held by the slip.
Bottom-hole assemblies appended to the bottoms of drill strings are usually made up of many tools or components. Examples of such components include the drill bit, drill collars, shock subs, jars, mud motors, measurement-while-drilling tools, stabilizers and others. These components have different diameters such that, to suspend the bottom hole assembly (“BHA”), many different configurations of the suspension assembly are required in the rotary table. During a single run of a BHA into a borehole, slips, bushings, insert bowls and other components of the suspension assembly may have to be removed and replaced multiple times in order to accommodate the different diameters of the BHA components. These multiple removals and replacements usually require manual handling of heavy components with lifting slings, which is a time consuming and labor intensive operation where procedures aimed at personnel safety must be consistently followed. Further, contemporary rig usage cost is on the order of many thousands of dollars per hour, thus time consuming operations are to be avoided wherever possible. Accordingly, there remains a need in the art for improved methods of efficiently and safely grasping and suspending well strings in a borehole.